1. Field of the Invention
The present invention relates to a hybrid vehicle having an internal combustion engine and a motor as a vehicle drive source, and, more particularly, to an apparatus for controlling the hybrid vehicle.
2. Description of the Related Background Art
Hybrid vehicles having an engine and a motor as a drive source are known. A control apparatus for controlling such a hybrid vehicle is disclosed in Japanese Laid-Open Patent Publication No. 3(1991)-121928, for example.
The control apparatus drives a motor in accordance with the operating condition of a vehicle as well as controls the output of an engine. Specifically, the operation mode of the motor is determined in accordance with the operating condition of the vehicle. In the acceleration mode, electric drive power is supplied to the motor to perform an assist operation for assisting the output of the engine. In the deceleration mode, regenerative operation is performed to store regenerative electric power produced by the motor to a capacitor as a high-voltage storage device. The electric power stored in the capacitor is used as electric power motor drive in the assist operation.
Recently, other than the acceleration mode and deceleration mode, a cruising mode for controlling a constant speed of a vehicle has been suggested. In the cruising mode, either the assist operation or regenerative operation is selectively performed by taking into account operating conditions such as the speed of the vehicle and the state of the capacitor charge.
However, it has been a difficult problem to distinguish clearly between the acceleration mode and the cruising mode in accordance with the operating conditions of a vehicle. That is, it was necessary to distinguish the operating conditions under which the operation mode of the motor is to be changed from the acceleration mode to the cruising mode and the operating conditions under which the operation mode is to be changed from the cruising mode to the acceleration mode, so as to improve fuel consumption of the engine and ensure drivability.